The overall layout of conventional vegetation trimmers can best be understood by reference to the accompanying FIGS. 1 and 2, in which the parts of the trimmers shown therein are labelled as follows:
10Motor20Cutting head30Drive shaft50Front handle60Rear handle70Fulcrum
The two heaviest components of a vegetation trimmer are generally the cutting head and the motor. In operation, the trimmer is typically swung from side to side by a user by a twisting motion of the body and arms of the user about the fulcrum 70, in the manner indicated by the arrowed arcs A and B shown in FIGS. 1 and 2.
Most conventional vegetation trimmers have the layout shown in FIG. 1. In this configuration, both the motor and the cutting head are located at the bottom end of the trimmer and a rigid drive shaft is used to connect the output of the motor to the cutting head. There may also be a gear train located between the motor and the cutting head to change the rate of rotation. In this case, the two heaviest components of the trimmer are both located at the bottom end of the trimmer.
However, some conventional vegetation trimmers have the different layout shown in FIG. 2. In this configuration, only the cutting head is located at the bottom end of the trimmer and the motor is instead located at the top end. Because the two heaviest components of the trimmer are now located at its opposite ends, the trimmer of FIG. 2 is better balanced than the trimmer of FIG. 1. However, because in the configuration of FIG. 2, the output from the motor is no longer parallel with the axis of rotation of the cutting head, a flexible drive shaft must be used instead of a rigid drive shaft to transfer the output of the motor to the cutting head. Once again, there may also be a gear train located between the motor and the cutting head to change the rotation speed. This flexible drive shaft is typically constructed from layers of wound wire as shown in FIG. 3 and as a result, is somewhat like a stiff spring.
However, both of the conventional layouts of vegetation trimmer shown in FIGS. 1 and 2 have certain disadvantages relating to their balance and inertia which are explained in greater detail below.